1. Field of the Invention
The invention relates to a display apparatus having an active matrix driving type display panel.
2. Description of Related Art
Recently, an electroluminescence display apparatus (hereinafter, referred to as an EL display apparatus) is drawing attention, in which a display panel using an organic electroluminescence device (hereinafter, referred to as an EL device) is mounted as a light emitting device including pixels. As the driving scheme for the display panel by the EL display apparatus, an active driving type system is known.
FIG. 1 is a diagram schematically showing the construction of an active driving type EL display apparatus.
As shown in FIG. 1, the EL display apparatus is constituted by a display panel 10 and a driving apparatus 100 for driving the display panel 10 with a video signal.
The following elements are formed on the display panel 10: a common ground electrode 16; a common power electrode 17; scanning lines (scanning electrodes) A1 to An serving as n horizontal scanning lines of one screen; and m data lines (data electrodes) D1 to Dm arranged to cross the scanning lines, respectively. Active driving type EL units E1,1 to En,m functioning as pixels are formed in the crossing portions of the scanning lines A1 to An and the data lines D1 to Dm, respectively. A power voltage VA to drive the EL units E is applied to the common power electrode 17. The common ground electrode 16 is connected to the ground.
FIG. 2 is a diagram showing an example of the internal construction of one EL unit E formed in the crossing portion of one scanning line A and one data line D.
In FIG. 2, the scanning line A is connected to the gate of an FET (Field Effect Transistor) 11 for selecting the scanning line and the data line D is connected to the drain of the FET 11. The gate of an FET 12 for light emission driving is connected to the source of the FET 11. The power voltage VA is applied to the source of the FET 12 via the common power electrode 17. A capacitor 13 is connected between the gate and the source of the FET 12. Further, an anode terminal of an EL device 15 is connected to a drain of the FET 12. A cathode terminal of the EL device 15 is connected to the ground via the common ground electrode 16.
The driving apparatus 100 sequentially applies scanning pulses to the scanning lines A1 to An of the display panel 10 in an alternative way. The driving apparatus 100 further generates pixel data voltages DP1 to DPm corresponding to the horizontal scanning lines based on the incoming video signal and applies those voltages to the data lines D1 to Dm in synchronism with the timing of the application of the scanning pulses, respectively. In this process, each EL unit connected to the scanning line A to which the scanning pulse has been applied becomes a writing target of the pixel data. The FET 11 in the EL unit E serving as a writing target of the pixel data turns on in response to the scanning pulse and applies the pixel data voltage DP supplied via the data line D to the gate of the FET 12 and to the capacitor 13, respectively. When the pixel data voltage DP is low, the FET 12 supplies a predetermined light emission drive current Id which is generated based on the voltage VA to the EL device 15. The EL device 15 emits light at a predetermined luminance in accordance with the light emission drive current Id.
When the gate-source voltage/output current characteristic of the FET 11 is shifted due to a temperature-related change, a change with the passage of time, or the like, even with a fixed gate source voltage VGs(=the power voltage VA−a gate voltage G) a fluctuation of the output current, that is, the light emission drive current Id occurs. This occurrence results in the fluctuation of the luminance of the EL device 15. The power voltage VA has previously been set to a lightly high voltage in consideration of the increased amount of a forward voltage due to the temperature-related change, change with the passage of time, or the like in the EL device 15. Therefor, the loss of electric power increases at the initial stage or at a standard state.